1. Field of the Invention
This invention pertains to laminated safety glass, especially for an airplane pressurized cockpit window, including at least two sheets of glass and a separating layer made of plastic.
2. Description of the Background Art
Laminated glass windows in airplanes, that is to say windows which include at least two sheets of glass and a separation layer made of plastic which is formed by one or several sheets of polyvinylbutyral and/or polyurethane, can be installed by being bolted together in the structure of the cockpit as described, for example, in U.S. Pat. No. 3,616,122, or more simply by being fitted into a rabbet.
In flight these windows are subjected to considerable differential pressure between the inside and outside of the cockpit. This differential pressure must be maintained under all circumstances, particularly in case of a flight incident causing breakage of the window.
Thus, laminated glass windows for airplanes use at least two sheets of glass as structural layers to mitigate the consequences of accidental breakage of a sheet of glass. Each of them must be capable of supporting the maximum differential pressure to which the airplane window might be subjected during flights at high altitude.
Although not likely, a fracture of two sheets of glass which constitute the structural layers is nevertheless possible. When the window is bolted to the structure of the cockpit, it can remain in place even if the sheets of glass break, due to the separating layer which itself is held by the bolts. On the other hand, if the window is installed by being fitted into a rabbet, this might cause exposure of the window base in case of breakage of sheets of glass, which will result in sudden depressurization through the opening that is thereby made.